1. Field of the Invention
The present invention relates to a telephone communication system, and in particular to an apparatus and method for preventing unauthorized access to a long distance carrier.
2. Description of Related Art
The telephone call security system of the invention takes advantage of a local telephone company's ability to completely block default access to a long distance carrier's direct dial network or operator service. Long distance carrier access is commonly routed through an access switch controlled by a computer which operates the switch to permit or deny access to the carrier system. However, a problem has arisen in that it is possible to gain unauthorized access through the use of wiretaps or illegal telephone extensions.
While it is possible to limit an authorized telephone to a list of permitted telephone numbers by using telephone hardware and software alone, telephone-resident security systems may be by-passed by simply placing the wiretap or unauthorized extension downstream of the authorized telephone on the local telephone line. The present system therefore operates at the system level, and in particular at the long distance carrier access switch.
Recently, telephone systems have been implemented which, when a telephone call is made from a restricted access telephone such as a pay phone to the access switch control system, have the capability of analyzing the telephone number dialed, sending rate information to the telephone, and controlling access based on a signal from the telephone that sufficient money has been deposited into escrow for the call.
Such dialogues between the telephone and the switch control system commonly make use of the Dual Tone MultiFrequency (DTMF) system of tones, in which each tone or sequence of tones is assigned a specific meaning. This is the type of system used by most "touch tone" telephones.
Despite the sophisticated hardware and software used in such access systems, however, they can nevertheless be defeated by either tampering with the telephone or placing a wire tap or unauthorized extension on the telephone line, as noted above. Because the conventional DTMF "dialogue" can be relatively easily duplicated, it is often impossible for a conventional switch control system to determine whether a request for access to the long distance carrier originates from an authorized telephone. Losses resulting from fraudulent access continue to be a significant problem for long distance carriers.